Friday, May 29, 2009

As the khatri veyyil' ends, Chennaiites can heave a sigh of relief. May, traditionally the hottest month, has been comparatively pleasant.

Reason? The sea breeze blew in early enough to contain the heat radiation. Unlike in the previous two years, the mercury touched 40 degrees Celsius only on four days this year. In 2007, it climbed over 40 C on 12 days, and last year it touched 40 and above on 16 days. The pleasanter weather

has come in a year when summer showers have been deficient. According to the Met department, Nungambakkam recorded 17 mm of rain between March and May while Meenambakkam was deficient by 42 mm, as against the normal 79 mm.

"The timely onset of the sea breeze has kept the temperature under control, since clear skies and sea breeze control heat radiation," said Y E A Raj, deputy director-general of meteorology, Regional Meteorological

Centre (RMC). "When the sea breeze sets in, the day temperature will drop by two or three degrees in one hour, and since they blow for 12 hours a day in May, the weather will be pleasanter," he added. According to him, strong westerly winds will impede the onset of sea breeze, and make the temperature warmer. Barring on May 13, 14, 23, and 25, the arrival of sea breeze has been close to normal. In May 1910 and in May 2003, Chennai recorded 45 degrees Celsius.

According to RMC director S R Ramanan, "A low pressure blocked a good part of the solarradiation and aided in maintaining comfortable levels this May."

A Ramachandran, director, Centre for Climate Change and Adaptation, Anna University, pointed to a 0.2 degree rise in the mean value of day temperatures during the khatri over the last two decades. According to him, man-made causes are likely to impact radiation levels in future

May 28 Weather conditions seem to have reverted to pre-monsoon coordinates with a signature north-south trough (or wind discontinuity) reappearing along 'the trunk' of mainland India.

The northern limit of monsoon as on Monday passed through Mangalore, Dharmapuri, Chennai, Paradip, Balasore, Bankura and Gangtok. No further progress has been made ever since.

UNSTABLE WEATHER

Opposing wind streams from the northwest and the southeast of the peninsula merge along the formation and cause instability. The IMD has forecast rain or thundershowers in the region over the next three days.

Residual moisture from erstwhile cyclone Aila is available over east and northeast of the country. Rain or thundershowers are possible at a few places over the Indo-Gangetic plains until Sunday. This would also bring down maximum temperatures by 2-4 deg Celsius over the region.

ANDAMAN RAINS

Meanwhile, isolated heavy rainfall has been warned of over Andaman and Nicobar Islands during the next two days. The Canadian Meteorological Centre saw a circulation spinning up here and heading north-northeast to drive rains into southern Myanmar by Sunday.

The Thailand Met Department observed that 'rather strong' monsoon prevailed over the Andaman Sea and the Thai Gulf on Thursday. Torrential rainfall has been warned of in the region with isolated heavy spells. Ships have been advised to proceed with cation until Sunday. A 24-hour forecast spoke of 'very cloudy' conditions with fairly widespread thundershowers and isolated heavy rain. Southwesterly winds may reach speeds of up to 35 km/hr. Fresh activity would be triggered in the Arabian Sea also during the next three days, an IMD outlook said.

PACIFIC CYCLONE

The Climate Prediction Centre (CPC) of the US National Weather Services said enhanced rainfall is likely over the Arabian Sea, southern India to Southeast Asia during the week ending June 1.

It attributed this to the prevailing Indian and Southeast Asian monsoon, above-normal sea-surface temperatures in some areas and interaction with an extra-tropical circulation (westerly system to the north of Himalayas but mainly impacting south-east Asia).

In what is being seen as prejudicial to monsoon over mainland India, the CPC sees the threat of tropical cyclone development for parts of South China Sea (just east of the Bay of Bengal) and adjoining west Pacific.

A tropical cyclone spinning up could do to the monsoon what Tropical Cyclone Aila has already managed to disrupt wind flows and appropriate incoming moisture to itself.